Plagioclase
/ˈpleɪ.dʒi.oʊ.kleɪz/noun
A major group of rock-forming feldspar minerals that form a continuous series between sodium-rich and calcium-rich compositions.
Did you know?The name was coined in the 19th century from Greek roots because these feldspars split along cleavage planes that are not perfectly right-angled, making the word a scientific description of a physical “angle” rather than a mystical one.
Etymological Timeline
Ancient Greek
Greek
plagios
“oblique, slanting, sideways”
Ancient Greek
Greek
klasis
“a breaking or fracture”
19th Century
German/Scientific Latin
Plagioklas
“a feldspar characterized by oblique cleavage”
19th Century
English
plagioclase
“a group of feldspar minerals with oblique cleavage”
Modern English
English
plagioclase
“a major rock-forming feldspar mineral series”